The present invention broadly relates to joining sheet metal or sheet material and, more specifically, pertains to a new and improved method and apparatus for bringing together or uniting the edges or edge regions of a blank or panel of sheet metal or sheet material
In the present invention the edges of the sheet metal blank, which is rolled or formed substantially to a cylinder, are brought together during transport of the formed or rolled blank or panel from a forming or rolling machine to a joining or welding station. The welding station is preceded by a guide apparatus serving for conducting the formed or rolled panel into the welding station. The rolled or formed cylinder has a longitudinal axis or axis of rotational symmetry. The guide apparatus comprises a substantially bar-shaped support member or body arranged immediately before the joining or welding station and containing two lateral guide slots for the edges of the blank or panel of sheet metal or sheet material. The two guide slots each have an entry end and an exit end and mutually converge from the entry end to the exit end.
Guide devices, also known as Z-rails, are known from the general state of the prior art and are especially employed in welding together the edges of blanks or panels of sheet metal rolled to cylindrical or tubular bodies and in which the sheet metal edges mutually overlap. Such guide rails are provided with two straight slots guiding both sheet metal edges and inducing the sheet metal edges to overlap. These slots initially have a mutual vertical spacing which then decreases toward the end of the rail. The bases of both slots contain a greater spacing in the horizontal direction initially than at the end of the rail, so that the sheet metal edges guided in the slots can be conducted out of a relatively great overlap into a desired and precisely predetermined lesser overlap (cf. Swiss Patent No. 602,255, granted July 31, 1978).
It is furthermore also known in the art to provide such Z-rails with a pivotable end piece in order that the sheet metal edges exiting from the slots at the ends of the Z-rail can be oriented very precisely in relation to the clamping line between both electrode rollers of the welding machine without the sheet metal edges having to be even slightly deflected at the welding location after leaving the Z-rail (cf. German Pat. No. 2,839,407 and the cognate U.S. Pat. No. 4,214,140, granted July 22, 1980). The pivotable end piece, which is severed from the initially integrally fabricated Z-rail and subsequently reconnected thereto by a hinge, comprises, as does the principle component, straight slots converging toward the end of the Z-rail.
For butt-welding two cut edges, Z-rails are also employed in which the cut edges are initially spaced vertically in relation to one another as in the previously mentioned rail, but which do not, however, mutually overlap but are held precisely in a common vertical plane and are brought into edge contact at the end of the Z-rail (cf U.S. Pat. No. 4,354,090, granted Oct. 12, 1982).
The edges of exactly cut blanks or panels of sheet metal can be rapidly and reliably brought together by this know device and conducted to an energy beam welding location (e.g. laser, electron beam, and so forth) and butt-welded.
It is very difficult and expensive to produce absolutely straight cut edges outside of the laboratory at high production rates, since even the slightest deviations in concentricity of the cutter wheels or disks of the currently very commonly employed rolling shears cause a wobble effect of the cutting edges of the wheels or disks and therefore produce a curved or arcuate course or extent of the cut edges they produce. When bringing together or butting such blanks or panels with so-called curved cuts or bowed edges, the edges to be welded together therefore no longer lie flush against one another over the entire length. This can lead to faulty welds or, if the arc height is so great that the edges lie far apart, to unwelded zones along the locus of the joint.
Furthermore, the still unwelded blank or panel edges tend to spread apart from one another during the welding process. In order to compensate this spreading effect, it has been proposed in Z-rails for overlap welding machines to conduct the blank or panel edges initially overlapping more than necessary, i.e. more than the amount of overlap at the weld location and to bring them to the desired actual value only immediately at the welding location In this manner the spreading effect can be compensated.
This measure for butt-welding can not be employed for slightly curvedly cut or bowed blank or panel edges, since the deficiency of sheet metal in the bowed region can not be supplied by this measure.
In order to be able to hold together both blank or panel edges overlapping in practice by less than a millimeter, pressure means must be provided in this region, e.g. a calibrating roller ring, which firmly guides the tubular sheet metal body. Firm guidance of the thin sheet metal body has great disadvantages, since high friction arises in the slots of the Z-rail due to the high pressure of the sharp panel edges, and heavy wear therefore occurs and scratches can arise on the surface of the sheet metal body.